Dispersion-controlled polymers for broadband fiber optic devices

ABSTRACT

Novel polymer compositions for controlling or correcting dispersion mismatch between the composition and a side-fiber polished optical fiber are disclosed. The polymer compositions contain an infrared absorbing dye having an absorption maximum from about 900 to about 1200 mn and and a polar olefin copolymer containing monomers which are formed from polar olefins having an ester, benzene, or halogen substituent attached. A method for controlling the dispersion exhibited by the novel polymer compositions is also disclosed. The method includes forming the polymer composition over an exposed surface of an optical fiber. Dispersion is controlled by controlling the amount of dye present in the polymer composition. Also disclosed is an optical device from which improvements in the uniformity of spectral response and performance are observed across a wavelength band. The optical device includes the polymer composition formed over an optical fiber. Variable optical attenuators, switches, and couplers can be designed which incorporate the polymer compositions. The invention is particularly useful in the 1500-1600 nm wavelength band.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of earlier U.S. patent application Ser.No. 09/139,457, filed Aug. 25, 1998, now U.S. Pat. No. 6,191,224.

Each of these Applications is hereby incorporated by reference herein inits entirety.

TECHNICAL FIELD

The present invention relates to polymeric materials formulated tocontrol optical dispersion, and more particularly, to the use of thesedispersion-controlled polymeric formulations in broadband fiber opticdevice applications.

BACKGROUND OF THE INVENTION

Dense wavelength division multiplexed (DWDM) optical networks increasetheir transmission capacity by employing multiple co-propagating,discrete, wavelength channels, each carrying independent data streams.Broadband fiber optic devices, such as variable attenuators, couplers,and switches having a controllable spectral response, are criticalcomponents of DWDM systems. Currently, DWDM systems operate in the 1550nm spectral region because of the availability of optical amplifierscontaining erbium-doped optical fibers. However, as amplifier technologydevelops, and capacity demands increase, DWDM systems are expected toexpand their spectral extent and increase their channel density.

Optical power, as it propagates in a single-mode optical fiber, or anyother waveguide or bulk material, experiences dispersion, i.e. differingwavelengths propagate at different speeds. In an optical fiber, modalextent and phase velocity are affected by both the dispersion of thematerial (material dispersion) and the dispersion of the waveguide(waveguide dispersion) causing the light to pass through at differentspeeds. Thus, across a given wavelength region, differences between thedispersions of the material and waveguide through which light propagatescan result in nonuniform spectral performance of fiber-based devices.

Dispersion is often represented in terms of a material's refractiveindex (n) as a function of optical wavelength (λ), i.e. as n(λ). Indispersive materials, the refractive index of the material changes withwavelength. The relevant parameter when describing modal dispersion ormultimode distortion in optical fibers is the effective mode index, alsoreferred to herein as “effective mode dispersion”, n_(eff)(λ), which, insimple waveguide geometries, can be calculated using the materialdispersion of the fiber's cladding and core, n_(clad)(λ) andn_(core)(λ), respectively, and geometric parameters. Sellmeierdispersion equations for the cladding and core in a single mode opticalfiber are provided by J. Gowar, in Optical Communication Systems, ch. 3,58-77 (2d ed.993). For a glass fiber, the material dispersions for thecladding and core are calculated from the following Sellmeier equations(1 a) and (1 b), respectively, which are valid from 0.3-3.0 μm:$\begin{matrix}{{{{n_{clad}^{2}( {\lambda \lbrack {\mu \quad m} \rbrack} )} - 1} = {\frac{0.6962\lambda^{2}}{( {\lambda^{2} - 0.0684^{2}} )} + \frac{0.4970\lambda^{2}}{( {\lambda^{2} - 0.1162^{2}} )} + \frac{0.8975\lambda^{2}}{( {\lambda^{2} - 9.8962^{2}} )}}}} & ( \text{1a} ) \\{{{n_{core}^{2}( {\lambda \lbrack {\mu \quad m} \rbrack} )} - 1} = {\frac{0.7192\lambda^{2}}{( {\lambda^{2} - 0.0709^{2}} )} + \frac{0.3988\lambda^{2}}{( {\lambda^{2} - 0.1157^{2}} )} + \frac{0.9099\lambda^{2}}{( {\lambda^{2} - 9.9093^{2}} )}}} & ( \text{1b} )\end{matrix}$

The dispersions of the cladding, n_(clad)(λ) and core, n_(core)(λ), andthe effective mode dispersion, n_(eff)(λ) for a silica glass opticalfiber having a core with a slightly raised refractive index relative tothe surrounding cladding are plotted in FIG. 1. Although all materialsare dispersive to some extent, a hypothetical material exhibiting nodispersion would be represented in the graph of FIG. 1 as a horizontalline. The greater the dispersion, the steeper the slope (negative orpositive). As used herein, the term “dispersion” refers to the slope ofthe line formed from a plot of a material's change in refractive indexversus change in wavelength. As can be seen from the slope of n_(eff)(λ)in FIG. 1, a single mode optical fiber is dispersive.

Because the effective mode index is dispersive, fiber-based devices mayexhibit spectrally non-uniform performance, which is undesirable formany broadband device applications. An example of this is aside-polished fiber (SPF)-based attenuator. Cargille Refractive IndexLiquids, which may be coupled onto the attenuator, each have awell-characterized refractive index, n_(D), where subscript D denotesthe Sodium D-Line wavelength (λ=589 nm), and a well-characterizeddispersion curve. As disclosed in copending commonly assigned U.S.application Ser. No. 09/026,755 entitled “Fiber Optic Attenuators andAttenuation Systems”, the disclosure of which is incorporated herein byreference, placing a coupling oil (n_(D)=1.456 at 27.9° C.) on a SPFcoupler induces power loss (attenuation). FIG. 2a is a plot ofattenuation (optical energy transmission) in decibels versus wavelength(1520-1580 nm) for a SPF coupler having a 95% polished cladding level.As shown in FIG. 2a, the attenuation is not uniform across the spectralregion. This spectral nonuniformity is observed because the dispersionof the oil, n_(oil)(λ), which is calculated from equation (2) as$\begin{matrix}{{n_{oil}( {\lambda \lbrack Å\rbrack} )} = {1.44418 + \frac{401173.2}{\lambda^{2}} + \frac{3.18914 \cdot 10^{11}}{\lambda^{4}} - {{3.89 \cdot 10^{- 4}}( {{T\lbrack {{^\circ}\quad {C.}} \rbrack} - 25} )}}} & (2)\end{matrix}$

(where T is the temperature) is mismatched to that of the fiber,n_(eff)(λ). This dispersion mismatch is depicted in FIG. 2b, where theslope of n_(oil)(λ) differs from that of n_(eff)(λ). By contrast, if thedispersion of the oil matched that of the fiber, the graphicrepresentations of the corresponding dispersions would be approximatelyparallel, and the attenuation would be almost constant or substantiallyuniform across the wavelength band with only small variations beingobserved.

As disclosed in the aforementioned U.S. application Ser. No. 09/026,755,certain organic polymers having an index of refraction close to that ofthe fiber can be applied to the exposed surface of a SPF optic for usein variable optical attenuators (as described below) Such polymersexhibit a change in refractive index proportional to a change intemperature. OPTI-CLAD® 145, which is available from Optical PolymerResearch, Inc. is an example of such a polymer. Although the refractiveindex of such organic polymer materials can be altered at a givenwavelength to match that of the fiber, the use of known polymers islimited in broadband applications because of the dispersion mismatchbetween the polymer and the fiber across the wavelength band ofinterest.

Control over the spectral response of a broadband fiber optic device canbe strongly dependent on the dispersion mismatch between the fiber andany coupling materials present. Therefore, polymer formulations aredesirable that would allow not only control of the refractive index ofthe polymer overlying the optical fiber, but also control of thedispersion properties of the polymer. Such dispersion control wouldpermit correction of the polymer's dispersion to substantially matchthat of the fiber and, alternatively, would allow the dispersion of thepolymer to be controllably altered from that of the fiber. Suchdispersion controllable materials would be useful in broadbandapplications, such as in the 1500-1600 nm region, where control ofspectral response is important. In addition, dispersion controllablepolymer materials would be useful in the fabrication of many broadbandfiber optic devices, such as variable optical attenuators (VOAs),couplers, and switches.

SUMMARY OF THE INVENTION

The present invention meets the aforementioned needs and is based on theunexpected discovery that certain polar polyolefin polymers doped withinfrared absorbing dyes having an absorption maximum from 900 to 1200 nmcan be formulated to correct or control dispersion mismatch between thepolymer and a fiber optic. The dye additives are used to control thedispersion from almost no difference in dispersion between the polymercomposition and the fiber optic to very strong differences indispersion. In addition, the refractive index of the novel polyolefincompositions of the present invention can be controlled and can bealtered to match or differ from that of the optical fiber. The noveldispersion-controlled polymer compositions of the present invention areparticularly useful in the fabrication of spectrally uniform fiber opticdevices such as VOAs, couplers, and switches for use in the 1500-1600 nmregion.

Accordingly, in one aspect, the present invention is adispersion-controlled polymer composition comprising:

(a) from about 0.2 to about 4% by weight of an infrared absorbing dyehaving an absorption maximum from about 900 to about 1200 nm; and

(b) from about 96.0 to about 99.8% by weight of a polar olefin copolymercomprising monomeric units derived from two or more polar olefins havingan ester, benzene, or halogen substituent attached thereto. The polarolefin copolymer preferably has a molecular weight from about 1,500 toabout 100,000 g/mole, with an upper limit of about 50,000 g/mole beingmore preferable, and an upper limit of about 5,500 g/mole being the mostpreferable.

The infrared absorbing dye is preferably:

(8-((3-((6,7-dihydro-2,4-diphenyl-5H-1-benzopyran-8-yl)methylene)-2-phenyl-1-cyclohexen-1-yl)methylene)-5,6,7,8-tetrahydro-2,4-diphenyl-1-benzopyryliumtetrafluoroborate or a metal complex dye having the general formulabis[1,2-[(4-alkyl¹ alkyl² amino)phenyl]-1,2-ethylenedithiolate]Met.Alkyl¹ and alkyl² are each independently lower alkyls containing 2 to 8carbon atoms. In addition, alkyl¹ may differ from or may be the same asalkyl². Met is a Group IIIB metal, preferably nickel, palladium orplatinum. The most preferable metal complex dyes includebis[1,2-(4-dibutylaminophenyl)-1,2-ethylenedithiolate]nickel;bis[1,2-[4-(ethyl heptyl amino)phenyl]-1,2-ethylenedithiolate]nickel;bis[1,2-(4-dibutylaminophenyl)-1,2-ethylenedithiolate]platinum; andbis[1,2-[4-(ethyl heptyl amino)phenyl]-1,2-ethylenedithiolate]platinum.

The polar olefins, from which the monomeric units of the copolymer arederived, are preferably selected from, but not limited to:

tetrafluoropropyl acrylate, tetrafluoropropylmethacrylate, butylacrylate, hexyl acrylate, trifluoroethyl methacrylate, lauryl acrylate,pentafluorostyrene, pentafluorophenyl acrylate, methyl acrylate,N,N-dimethylacrylamide, pentafluorophenyl methacrylate, methylmethacrylate, and vinylidene chloride.

In another aspect, the present invention is a method for controllingdispersion in the aforementioned novel polymer composition across awavelength band, the most preferable wavelength band being from about1500 nm to about 1600 nm. The first step of the method is providing aportion of an optical fiber through which optical energy can propagate.The portion of the optical fiber has material removed from it, therebyexposing a surface thereof. The portion of the optical fiber has aneffective mode refractive index at each wavelength of the wavelengthband and an effective mode dispersion across the wavelength band.

In the second step of the method, the polymer composition is formed overthe exposed surface of the portion of the optical fiber. The polymercomposition has a material refractive index at each wavelength of thewavelength band and a material dispersion across the wavelength band. Byaltering the amount of the infrared absorbing dye present in the polymercomposition, the material dispersion across the wavelength band iscontrolled to substantially match or mismatch the effective modedispersion of the optical fiber. Also, the amount of dye, as well as theparticular polyolefin contained in the polymer composition, controls thematerial refractive index at each wavelength. For substantial broadbanddispersion matching, two conditions must be met: 1) the materialrefractive index of the polymer composition must be substantially thesame as the effective mode refractive index; and 2) the change inrefractive index across the wavelength band of interest (i.e. slope)must be substantially the same for both the optical fiber and thepolymer composition. For example, a polymer composition which issubstantially dispersion-matched with an optical fiber preferably has amaterial refractive index which is controlled to lie within about 0.5%of the effective mode refractive index, more preferably within about0.2%, and most preferably within about 0.15%. In addition, tosubstantially match the dispersion of the fiber optic, the change inmaterial refractive index with wavelength is, for example, preferablywithin about 25% of the change in effective mode refractive index acrossthe wavelength band of interest.

The method may optionally include the step of altering the materialrefractive index to a desirable refractive index without changing thematerial dispersion. This may be accomplished by controllably changingthe temperature of the polymer composition formed on the surface of theoptical fiber.

In another aspect, the present invention is an optical device comprisinga portion of an optical fiber having material removed therefrom, therebyexposing a surface thereof, and the novel polymer composition formedover the exposed surface of the optical fiber. Optical energy or lighttransmitted through the fiber can propagate through or be extracted fromthe exposed surface. The spectral response of the optical device acrossa wavelength band of interest may be controlled by controlling thematerial dispersion relative to the effective mode dispersion. Foruniform spectral response, the material dispersion substantially matchesthe effective mode dispersion.

In addition, the optical device may optionally include a temperaturecontrolling circuit coupled to the polymer composition, wherein thetemperature controlling circuit provides a controllable stimulus to thepolymer composition to change the temperature thereof. The temperatureof the polymer composition affects the material refractive index withoutaltering the material dispersion or the spectral response of the device.

Based on the present invention, dispersion mismatch between an overlyingpolymer and an optical fiber can be controlled and corrected, ifdesired. This control is possible through modification of thecomposition of the polymer overlay using an infrared absorbing dye, asdescribed above. In addition, improvement in spectral performance acrossa wavelength band is possible. The availability of the presentdispersion and refractive index controlled polymer compositions can beused to develop novel fiber optical devices, such as attenuators,switches, and couplers.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the concluding portion of thespecification. The invention, however, both as to organization andmethod of practice, together with further objects and advantagesthereof, may best be understood by reference to the following detaileddescription of the preferred embodiment(s) and the accompanying drawingsin which:

FIG. 1 is a graph of refractive index versus wavelength (nm) depictingthe dispersions of the cladding and core for a glass optical fiber, andits effective mode dispersion;

FIG. 2a is a graph depicting attenuation in decibels versus wavelength(nm) for a SPF coupler having a 95% polished cladding level and acoupling oil (Cargille Labs, n_(D)=1.456);

FIG. 2b is a graph of refractive index versus wavelength (nm) depictingthe dispersion mismatch between the optical fiber and the coupling oilof the SPF coupler of FIG. 2a;

FIGS. 3a-b are respective graphs depicting the attenuation in decibelsversus wavelength (nm) for a polyolefin and for the same polyolefindoped with a dye, in accordance with the present invention;

FIG. 4a is a graph depicting the uniform attenuation in decibels versuswavelength (nm) for a polyolefin doped with a dye (polymer composition),in accordance with the present invention;

FIG. 4b is a graph of refractive index versus wavelength (nm) depictingthe dispersion matching between an optical fiber and the polymercomposition of FIG. 4a and also depicting the uniform attenuation indecibels versus wavelength (nm), in accordance with the presentinvention;.

FIG. 5a is a side, cross-sectional view of an optical device depicting aside-polished optical fiber and a polymer composition, in accordancewith the present invention; and

FIG. 5b is an end cross-sectional view of the optical device of FIG. 5a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to novel polymer compositions in whichdispersion can be controlled, a method for controlling dispersion of thepolymer compositions when overlaid on an exposed portion of an opticalfiber, and an optical device for controlling the optical power levelwith a uniform spectral response. The novel polymer compositions of thepresent invention are particularly useful in controlling the spectralresponse of fiber optic based devices within the wavelength band of1500-1600 nm.

The polar olefin polymers included in the novel polymer compositions ofthe present invention are copolymers containing monomeric units whichare derived from two or more polar olefins having an ester, benzene, orhalogen substituent attached thereto. As used herein, the term “polar”refers to the property in which the positive and negative electricalcharges of the olefin monomers are permanently separated, and the term“olefin” refers to the class of unsaturated aliphatic hydrocarbonshaving one or more double bonds. Polar olefin copolymers, also referredto herein as “polyolefins”, are easily synthesized from a variety ofcommercially available polar olefin monomers using conventionalpolymerization reactions, such as the one described below.

Illustrative useful monomers for inclusion in the polyolefins includethe preferred polar olefins listed above. Generally, for use incontrolling dispersion, a polyolefin is desired which has a refractiveindex, referred to herein as “base refractive index” that is close to,but lower than, that of the optical fiber (effective mode refractiveindex, n_(eff)). The effective mode refractive index is dependent uponthe fiber core and cladding indices, and the fiber core dimensions, butusually lies between the core and cladding refractive indices. For astandard glass fiber optic having an 8.3 μm diameter core region ofslightly raised refractive index surrounded by a 125±1 μm fused silicacladding, the effective mode refractive indices are shown in FIG. 1 forthe wavelength band from 1500 to 1600 nm. At 1500 nm, n_(eff) is about1.4466, and at 1600 nm, eff is about 1.4455. Typically, the baserefractive index of the undoped polyolefin has a value within about 1%of the effective mode refractive index.

Table 1 provides refractive index values, n_(D), where subscript Ddenotes the Sodium D-Line wavelength (λ=589 nm), for a variety of polarolefin monomers at room temperature (20-25° C). Within a wavelength bandof interest, blends of olefin monomers can be used for precise controlof the refractive index of the resulting polymer. More particularly, thebase refractive index of the polymer at each wavelength within the bandcan be controlled by adjusting the ratio and types of olefin monomersincluded in the polyolefin. Thus, there are many possible combinationsand amounts of polar olefins that can be used to form polar polyolefinshaving the desirable base refractive index. The relative amounts ofpolar olefin monomers contained in the polyolefin can be represented asratios or in terms of percent by weight (“% by weight” or “wt. %”). Itshould be noted that the invention is not limited to the use of themonomers listed above and in Table 1, and additional usefull polarolefin monomers having an ester, benzene or halogen substituent attachedthereto that can be used to obtain the desirable base refractive indexwould be obvious to one of skill.

TABLE 1 Monomer Description Refractive Index (n_(D)) tetrafluoropropylacrylate 1.400 tetrafluoropropylmethacrylate 1.400 butyl acrylate 1.418hexyl acrylate 1.428 trifluoroethyl methacrylate 1.437 lauryl acrylate1.445 pentafluorostyrene 1.450 pentafluorophenyl acrylate 1.470 methylacrylate 1.472 N,N-dimethylacrylamide 1.473 pentafluorophenyl 1.487methyl methacrylate 1.489 vinylidene chloride 1.600

In addition, the refractive index of the resulting polar olefincopolymer can be altered by heating or cooling the polymer to atemperature above or below its initial temperature or by controlling themolecular weight of the polymer. An increase in the temperature of thepolymer will lower the refractive index, and a decrease in thetemperature of the polymer will increase the refractive index. Themolecular weight of the polyolefin can be regulated by controlling theamount of chain terminating agent added during polymerization, asdiscussed below. To be useful, the novel polar olefin polymercompositions of the present invention preferably contain polyolefinshaving a molecular weight (Mw) from about 1,500 g/mole to about 100,000g/mole. However, the molecular weight (Mw) is more preferably from about1,500 to about 50,000 g/mole, and most preferably from about 1,500 toabout 5,000 g/mole.

The importance in controlling the aforementioned variables can beillustrated as follows. When designing an overlay material for avariable optical attenuator, control of polyolefin composition, itsmolecular weight and temperature determines the refractive index of thepolymer and therefore provides attenuation control of the materialsystem. Initially, the base refractive index of the polyolefin can becontrolled to be lower than that of the underlying side-polished fiber(n_(eff)) so that little or no attenuation of light occurs at a chosentemperature. However, as disclosed in the aforementioned U.S. patentapplication Ser. No. 09/026,755, when the temperature of the polymeroverlay is decreased below the initial temperature, the accompanyingincrease in the polymer's refractive index causes attenuation of lightin the fiber. More particularly, attenuation occurs when the baserefractive index of the polymer is close to or higher than that of thefiber. Thus, when a material with low refractive index is overlayed on afiber, attenuation can be induced through a change in temperature. Thetemperature at which attenuation begins at a particular wavelength isdetermined by the base refractive index of the polymer. This effect oftemperature on refractive index can be used to control the variableattenuation of light in an optical fiber.

Table 2 shows the effect of polymer composition on the temperature atwhich attenuation begins. Table 3 shows how the molecular weight of apolyolefin (50% by weight N,N-dimethylacrylamide and 50% by weighttetrafluorophenyl acrylate) effects the temperature at which attenuationbegins. The molecular weights reported in Table 3 were controlled by theaddition of different amounts of 1-dodecanethiol to the polymerizationreactions, as discussed below. GPC analyses of the polyolefins wereperformed to determine the molecular weights.

TABLE 2 Polyolefin Description Temperature at Which (% by weight)Attenuation Begins (° C.) 15% dimethylacrylimide  1 85%tetrafluoropropylacrylate 30% vinylidene chloride 12 70%tetrafluoropropyl acrylate 50% dimethylacrylimide 57 50%tetrafluoropropylacrylate 30% methyl methacrylate 77 70%pentafluoropropylacrylate

TABLE 3 Molecular Weight (Mw) of Polyolefin Temperature at Which(g/mole) Attenuation Begins (° C.) 43,654 57 12,368 46  5,269 36  2,05530

Consideration will now be given to the preparation of useful polarpolyolefins and the novel polymer compositions containing dye withpreferred parameters and illustrative methods. Unless otherwiseindicated, the reactants and reagents used in the reactions describedbelow are readily available materials. Such materials can beconveniently prepared in accordance with conventional preparatoryprocedures or obtained from commercial sources. Optical characterizationof the polyolefins and polymer compositions described herein was done byapplying the polymer or polymer composition as an overlay on aside-polished optical fiber. Optical characterization includedmeasurement of the temperature at which the polymer overlay causedattenuation, dispersion of the material, and range of attenuationpossible. Polymer overlays were developed for variable attenuation attemperatures ranging from −1° C. to 100° C. Dispersion from 1520 to 1580nm was controlled within slope ranges of −15 to +7 dB. In addition, itshould be noted that the embodiments included and described herein arefor illustrative purposes only, and the invention is in no way limitedto the embodiments used in the examples.

Synthesis and Characterization of Polyolefins

The free radical polymerization of polar olefin monomers for use in thepresent invention may be accomplished by mixing the desired ratio ofmonomers with a catalyst, such as 2,2′-azobisisobutyronitrile (about 2mole %), and a chain terminating reagent such as an alkyl thiol. As usedherein, “alkyl”, refers to saturated hydrocarbon residues containingtwenty or fewer carbons in straight or branched chains, as well ascyclic structures. Any alkyl thiol may be used as the chain transferagent, but due to its unobtrusive odor, 1-dodecanethiol is preferredDuring the process, the alkyl portion of the aforementioned alkyl thioldetaches from the thiol moiety and attaches to each end of the polymer,thereby terminating further polymerization. The amount of the chaintransfer agent added to the reaction controls the molecular weight ofthe polymeric product. Typically, from about 0.5 to about 20 mole % ofalkyl thiol chain transfer agent is added to the mixture, with about 10mole % being preferred. These amounts translate into polyolefins havingmolecular weights (Mw) that range from about 1,500 g/mole when 20 mole %1-dodecanethiol is used to about 50,000 g/mole when 0.5 mole % isemployed.

Process temperatures in the polymerization reaction are not critical andcan vary widely. The polymerization reaction may be conducted at roomtemperature or, alternatively at elevated temperatures up to about 150°C. The polymerization is carried out in an inert atmosphere over aperiod of time sufficient to produce the desired polymer in adequateyield. Reaction times are influenced by the reactants, reactanttemperature, the concentration of the reactants, catalyst, and otherfactors known to those of skill in the art. In general, reaction timescan vary between about 40 minutes for preparing polyolefin at elevatedtemperatures and about 10 hours at room temperature.

EXAMPLE 1

A shlenk tube was charged with 40% by weight tetrafluoropropylmethacrylate (TFPMA) and 60% by weight pentafluorophenyl acrylate(PFPA), and the reaction mxre was stirred with 2,2′azobisisobutyronitrile (about 2 mole %) catalyst, 1-dodecanethiol(10mole %) using a magnetic stir bar. The reaction vessel was cooled ina slurry of dry ice and ethanol, evacuated and blanketed with argon. Thereaction vessel was heated to approximately 70° C. for 20 minutes, thenheated to 100° C. for 20 minutes. The resulting polymer was stripped ofany residual monomer by heating to 150° C. under vacuum for about 20minutes. The molecular weight (Mw) of the polyolefin product, asdetermined by GPC, was about 4,500 g/mole.

EXAMPLE 2

The procedure of Example 1 is followed substituting 50% by weighttetrafluoropropyl acrylate (TFPA) and 50% by weight pentafluorophenylacrylate (PFPA) for the polar olefins.

EXAMPLE 3

The procedure of Example 1 is followed substituting 40% by weighttetrafluoropropyl methacrylate (TFPMA) and 60% by weightpentafluorophenyl methacrylate (PFPMA) for the polar olefins and using15 mole % 1-dodecanethiol as the chain transfer agent.

EXAMPLE 4

The procedure of Example 1 is followed substituting 60% by weighttetrafluoropropyl acrylate (TFPA) and 40% by weight pentafluorophenylmethacrylate (PFPMA) for the polar olefins and using 20 mole %1-dodecanethiol as the chain transfer agent.

Synthesis and Characterization of the Polymer Composition

Infrared absorbing dyes useful in the present polymer compositionsinclude those having an absorption maximum from about 900 to about 1200nm. However, to be useful, the dye should be soluble when added to thepolyolefin. One example of a suitable dye is(8-((3-((6,7-dihydro-2,4-diphenyl-5H-1-benzopyran-8-yl)methylene)-2-phenyl-1-cyclohexen-1-yl)methylene)-5,6,7,8-tetrahydro-2,4-diphenyl-1-benzopyryliumtetrafluoroborate having an absorption maximum (λ_(max)) at 1100 nm.This dye is available from Aldrich Chemical Co. and will be referred toherein as “IR1100”. Other preferred dyes include those having thegeneral formula bis[1,2-[(4-alkyl¹ alkyl²amino)phenyl]-1,2-ethylenedithiolate]Met, wherein “alkyl¹” and “alkyl²”are each independently a lower alkyl. Alkyl¹ and alkyl² may or may notbe the same lower alkyl. As used herein, “lower alkyl”, refers tosaturated hydrocarbon residues containing two to eight carbons instraight or branched chains, as well as cyclic structures when possible.“Met” refers to a Group VIIIB metal, such as nickel, palladium orplatinum. Bis[1,2-[(4-alkyl¹ alkyl²amino)phenyl]-1,2-ethylenedithiolate]Met is represented by the followingstructural formula (I):

It should be noted that when both alkyl¹ and alkyl² are the same, thenomenclature is typically altered. For example, when both alkyl¹ andalkyl² are butyl groups and Met is nickel, the metal complex is morecommonly referred to asbis[1,2-(4-dibutylamino)phenyl)-1,2-ethylenedithiolate]nickel, ratherthan bis[1,2-(4-butyl butylamino)phenyl)-1,2-ethylenedithiolate]nickel.This preferred embodiment is also referred to herein as “Ni(butyl)”.Ni(butyl) has an absorption maximum (λ_(max)) at 1164 nm. Anotherpreferred dye is bis[1,2-[4-(ethyl heptylamino)phenyl]-1,2-ethylenedithiolate]nickel, which is referred to hereinas “Ni(ethyl heptyl)”. The λ_(max) for Ni(ethyl heptyl) is at 1164 nm.In addition, similar dithiolate metal complexes can be used as dyes inwhich platinum is substituted as the metal. Such dyes includebis[1,2-(4-dibutylaminophenyl)-1,2-ethylenedithiolate]platinum (referredto herein as “Pt(butyl)” and bis[1,2-[4-(ethyl heptylamino)phenyl]-1,2-ethylenedithiolate]platinum (“Pt(ethyl heptyl)”), bothof which have an absorption maximum (λ_(max)) at 1087 nm. Theaforementioned bis(1,2-diaryl-ethylenedithiolate) metal-based complexesof structure (I) can be prepared using the method disclosed by U. T.Mueller-Westerhoff et al. in Tetrahedron 47, 909-932 (1991).

However, the invention is not limited to the use of the aforementionedinfrared absorbing dyes, which are provided for illustrative purposesonly. Other suitable dyes having the appropriate absorptions will beevident to those of skill.

The dye is added to the polyolefins described above in an amount thatcan vary, preferably, from about 0.2 to about 4% by weight. The additionof this amount of the dye will cause an increase in the refractive indexof the composition relative to that of the base refractive index. Thisincrease will depend on the amount and type of dye added. Preferably,for dispersion matching, an amount of dye will be added to increase therefractive index of the polymer composition (referred to herein as“material refractive index”) to a value that is within about 0.5% of theeffective mode refractive index of the fiber. More preferably, fordispersion matching with an optical fiber, the value of the materialrefractive index will be within about 0.2% of the effective moderefractive index, and most preferably, within about 0.15%.

After addition of the dye, the polymer composition for controllingdispersion contains from about 96.0 to about 99.8% by weight of thepolar olefin polymer. When IR1100 is used as the dye, the concentrationof the dye in the composition is preferably from about 1 to about 4% byweight to reach the desired material refractive index, and that of thepolyolefin is preferably from about 96 to about 99% by weight. Morepreferably, in compositions containing IR1100 dye, the concentration ofthe dye is from about 1.8 to about 2.3% by weight and that of thepolyolefin is from about 97.7 to about 98.2% by weight.

When either Ni(butyl) or Ni(ethyl heptyl) is included as the dye, thepreferable amount of dye present in the composition is from about 0.2 toabout 1.5% by weight, and the polyolefin is preferably from about 98.5to about 99.8% by weight. More preferably, the amount of Ni(butyl) addedis from about 0.7 to about 1.0% by weight, resulting in a compositionthat contains from about 99.0 to about 99.7% by weight polar olefinpolymer. The preferable amount of dye in the composition when Ni(ethylheptyl) is employed is from about 0.7 to about 0.9% by weight, whichresults in a composition that contains from about 99.1 to about 99.7% byweight polyolefin. Most preferably, for dispersion matching, theconcentration of Ni(ethyl heptyl) or is about 0.82% by weight, and thatof the polyolefin is about 99.2% by weight.

When either Pt(butyl) or Pt(ethyl heptyl) is the dye, the preferableamount included in the polymer composition is from about 1.8 to about2.1% by weight, and more preferably, about 1.9% by weight.

EXAMPLE 5

The polyolefin product of Example 1 having a Mw of about 4,500 g/molewas doped with 0.82% by weight of Ni(ethyl heptyl) dye to produce apolymer composition that was dispersion matched with a glass opticalfiber.

Table 4 shows the effect of dye additives to dispersion differencesbetween a fiber optic and various exemplary polyolefin compositions.Dispersion was measured as the change in attenuation in a side-polishedfiber attenuator from 1520 to 1580 nm at −15 dB attenuation.

TABLE 4 Dispersion Polyolefin Description Dye Additive (dB) 30 wt. %vinylidene chloride none −15 70 wt. % tetrafluoropropylacrylate 50 wt. %hexylacrylate none −14 10 wt. % methyl methacrylate 40 wt. %tetrafluoropropylacrylate 40 wt. % methyl methacrylate none −13.2 60 wt.% tetrafluoropropylacrylate 20 wt. % N,N-dimethylacrylamide none −11.480 wt. % tetrafluoropropylacrylate 40 wt. % hexylacrylate none −8 20 wt.% methyl methacrylate 40 wt. % tetrafluoropropylacrylate 30 wt. % methylmethacrylate 1.2 wt. % −3.2 70 wt. % pentafluorophenyl Ni(ethyl heptyl)methacrylate dye 50 wt. % hexylacrylate 2.1 wt. % −1.5 10 Wt. % methylmethacrylate IR1100 dye 40 wt. % tetrafluoropropylacrylate 40 wt. %hexylacrylate 2.1 wt. % −1.2 20 wt. % methyl methacrylate IR1100 dye 40wt. % tetrafluoropropylacrylate 20 wt. % N,N-dimethylacrylamide 1.87 wt.% 0.3 80 wt. % tetrafluoropropylacrylate IR1100 dye 30 wt. % methylmethacrylate 1.5 wt. % 0.5 70 wt. % pentafluorophenyl Ni(ethyl heptyl)methacrylate dye 30 wt. % vinylidene chloride 1.2 wt. % 2.7 70 wt. %tetrafluoropropylacrylate Ni(butyl) dye 10 wt. % butylacrylate 2.97 wt.% 3 30 wt. % methyl methacrylate IR1100 dye 60 wt. %tetrafluoropropylacrylate

As can be seen from Table 4, varying the type and amount of dye as wellas the types and amounts of polar olefins (from which the monomericunits of the polyolefins are derived) included in the polymercompositions of the present invention provides control of dispersionThus, in the case of attenuation, the dispersion of the polymercomposition can unexpectedly be adjusted using the aforementionedinfrared absorbing dyes to produce either highly disperse or spectrallyflat attenuation across a broad wavelength band.

Particularly preferred polymer compositions usefull for controlling orcorrecting dispersion of optical energy from a side-polished opticalfiber are found and described below in Table 5. The exemplarycompositions were prepared using the procedures of Examples 1 and 4outlined above for forming a polar polyolefin and adding a dye to thepolyolefin product. The polyolefins also included a terminating alkylresidue (C=12) appended at each end, which came from the addition of 1to 20 mole % 1-dodecanethiol during the polymerization reaction.

TABLE 5 Preferred Polymer Compositions Polymer Compo- Polyolefin sitionDye Additive (wt. %) Polyolefin Monomers (I) IR1100 ≈97.7 to 98.2 ≈20−50wt % DMMA (≈1.8 to 2.3 wt. %) wt. % ≈50-80 wt % TFPA (II) IR1100 ≈97.7to 98.2 ≈20-50 wt % DMMA (≈1.8 to 2.3 wt. %) wt. % ≈50-80 wt % TFPMA(III) Ni(ethyl heptyl) ≈99.1-99.3 ≈50-60 wt. % PFPA (≈0.7-0.9 wt. %) wt.% ≈40-50 wt. % TFPMA (IV) Ni(ethyl heptyl) ≈99.1-99.3 ≈40-70 wt. % PFPA(≈0.7-0.9 wt. %) wt. % ≈30-60 wt. % TFPA (V) Ni(ethyl heptyl) ≈99.1-99.3≈40-70 wt. % PFPMA (≈0.7-0.9 wt. %) wt. % ≈30-60 wt. % TFPMA (VI)Ni(ethyl heptyl) ≈99.1-99.3 ≈40-70 wt. % PFPMA (≈0.7-0.9 wt. %) wt. %≈30-60 wt. % TFPA (VII) Ni(butyl) ≈99.0-99.3 ≈50-60 wt % PFPA (≈0.7-1.0wt. %) wt. % ≈40-50 wt. % TFPMA (VIII) Ni(butyl) ≈99.0-99.3 ≈40-70 wt. %PFPA (≈0.7-1.0 wt. %) wt. % ≈30-60 wt. % TFPA (IX) Ni(butyl) ≈99.0-99.3≈40-70 wt. % PFPMA (≈0.7-1.0 wt. %) wt. % ≈30-60 wt. % TFPMA (X)Ni(butyl) ≈99.0-99.3 ≈40-70 wt. % PFPMA (≈0.7-1.0 wt. %) wt. % ≈30-60wt. % TFPA (XI) Pt(ethyl heptyl) ≈97.9-98.2 ≈70-90 wt. % PFPA (≈1.8-2.1wt. %) wt. % ≈10-30 wt. % TFPMA

The following abbreviations were used in Table 5:

DMMA=N,N-dimethylacrylamide

TFPA=tetrafluoropropylacrylate

TFPMA=tetrafluoropropyl methacrylate

PFPA=pentafluorophenyl acrylate

PFPMA=pentafluorophenyl methacrylate

Of the polymer compositions listed in Table 5, polymer compositions(III) and (XI) are most preferred for dispersion-matching with a fiberoptic. An even more preferred embodiment of polymer composition (III)contains about 0.82 wt. % Ni(ethyl heptyl) dye and about 99.18 wt. %polar olefin polymer, wherein the polar olefin polymer comprisesmonomeric units derived from about 60 wt. % PFPA and about 40 wt. %TFPMA. Another even more preferred composition (XI) contains about 1.9wt. % Pt(ethyl heptyl) dye and about 98.1 wt. % polar olefin polymercomprising monomeric units derived from about 80 wt. % PFPA and about 20wt. % TFPMA.

The advantages of the present polymer compositions can be seen in FIG.3, which provides a comparison between the spectral attenuation observedfor a polyolefin doped with a dye (FIG. 3b) and the same polyolefin withno dye added (FIG. 3a). As can be seen in FIG. 3a, when no dye is addedto the polyolefin, the attenuation is nonuniform across the wavelengthsfrom 1520 to 1580 nm, and there is dispersion mismatch (i.e. thedispersions are poorly matched) between the polymer and fiber optic. Bycontrast, as shown in FIG. 3b, when an infrared absorbing dye having anabsorption maximum between 900 and 1200 nm is added to the polyolefin inthe appropriate amount in accordance with the present invention,substantially uniform spectral attenuation is observed. In FIG. 3a,attenuation was measured at 7.7° C. for a polyolefin containing 40% byweight N,N-dimethylacrylamide (DMMA) and 60% by weight tetrafluorophenylmethacrylate (TFPMA). In FIG. 3b, 0.9 mole % Ni(ethyl heptyl) dye wasadded to the polyolefin of FIG. 3a, and attenuation was measured at 19°C. The substantially uniform attenuation shown in FIG. 3b is a result ofthe unexpectedly small difference in dispersion (i.e. the dispersionsare substantially matched) between the polymer composition of thepresent invention and a fiber optic.

The advantages of the present invention are also illustrated in FIGS.4a-b. FIG. 4a shows the spectral attenuation (dB), and FIG. 4b shows thedispersion across a dispersion matched material (40 wt. % DMMA, 60 wt. %TFPMA +0.9 mole % Ni(ethyl heptyl) dye at 19° C.) on a SPE coupler inaccordance with the present invention. Because the slope of the lineassociated with the fiber optic (n_(eff)(λ)) is substantially the sameas that of the polar olefin polymer composition, as shown in FIG. 4b,the materials are said to be “dispersion-matched” or “substantiallymatched”. When the dispersions of the optical fiber and polymercomposition are substantially matched, the spectral response, i.e.attenuation, remains substantially constant across a wavelength band,e.g. 1520 to 1580 nm, as shown in FIG. 4a.

The relationship of “dispersion mismatch”, which is the difference inthe slopes of the refractive index versus wavelength for a materialrelative to a fiber optic, to variation in spectral uniformity of theperformance of a side-polished fiber variable optical atttenuator isillustrated in the following Table 6. The calculations were performedusing the data shown in the graphs of FIGS. 3a-b. It should be notedthat the data reported in Table 6 are for illustrative purposes only,and that many variables and uncertainties will effect the informationcontained therein. However, because dispersion is well understood bythose of skill, one of ordinary skill in the art would know if materialsare substantially matched or mismatched. In addition, one of skill wouldbe able to adjust the dispersions according to particular spectralrequirements. It should also be noted that the invention is not limitedto variable attenuators, but is also useful in other applications, aswould be obvious to one of skill, such as in couplers and switches, forexample.

TABLE 6 Spectral Index Slope [nm⁻¹] Slope Nonuniformity Material(1500-1600 nm) Ratio (dB/nm) Fiber (and/or 1.167 × 10⁻⁵ 1.000 0.000Perfectly Matched Material) “Substantially 9.167 × 10⁻⁶ 0.786 0.017Matched” Polymer “Poorly Matched” 5.333 × 10⁻⁶ 0.457 0.167 Polymer

As is apparent from Table 5, the attenuation from a “poorly matched”material can be more than 10 times less uniform than a “substantiallymatched” material.

The present invention also includes a novel method for controllingdispersion of a polymer composition relative to an optical fiber, aswell as an optical device for controlling spectral response,particularly across the wavelength band of 1500-1600 nm The presentmethod and device incorporate the novel dispersion-controlled polymercompositions described above, which are positioned over an exposedsurface of an optical fiber. As a result of incorporating the presentpolymer compositions into the structure, the spectral response of thedevice becomes controllable and can be made substantially uniform. Thus,the performance of the device in which the dispersions of the fiber andpolymer composition are substantially matched is constant independent ofthe wavelength used. Because such a device is insensitive to thewavelength of light propagating across the fiber, the same response isobserved across the entire wavelength band of interest. The technologyenables dispersion mismatch between the fiber optic and polymer overlayto be controlled. Thus, for example, attenuators having constantattenuation across the wavelength band or spectral region can bedesigned, as well as couplers and switches.

In accordance with the present invention, an optical device 100 forcontrolling dispersion of light typically having a wavelength from about1500 nm to about 1600 nm is depicted in FIGS. 5a-b. In addition, thepresent method for controlling dispersion can best be understood withreference to the same drawings. According to the first step of thepresent method, a portion of a single-mode optical fiber (e.g.,telecommunications Corning SMF-28) 30 is provided in which material hasbeen removed to expose surface 65. The fiber is typically side-polishedthrough its cladding 50 close to its core 40, thereby exposing, throughsurface 65, an evanescent tail of the optical energy transmitted in thefiber. The remaining cladding thickness is generally <about 10 μm.However, the invention is not limited to the use of side-polishedoptical fibers, and other fibers having an exposed surface may be used.Fiber 30 has an effective mode refractive index at each wavelengthacross the wavelength band, which, as stated above, typically includeswavelengths from about 1500 to about 1600 nm.

In the second step, novel polymer composition 60 of the presentinvention, which is described above, is formed over polished surface 65of the fiber cladding. Optical energy propagating through the fiber canthen be extracted from the fiber core by polymer composition 60. Thepolymer composition may be prepared by polymerization of two or more ofthe above polar olefins, followed by doping with an infrared absorbingdye, as previously described. As previously stated, the base refractiveindex of the polyolefin may be controlled to be lower than the effectivemode refractive index of the fiber (preferably within 1%) by changingthe ratio of the polar olefins polymerized or by changing the molecularweight of the polar olefin polymer.

For correction of dispersion mismatch, polymer composition 60 isformulated, as described above, to have a material refractive index thatis substantially the same as the side-polished fiber's correspondingeffective mode refractive index (n_(eff)) at each wavelength within thewavelength band. In addition, for dispersion that is substantiallymatched, the slope associated with the polymer composition (i.e. changein material refractive index across the wavelength band) must besubstantially the same as that associated with the fiber optic (changein effective mode refractive index with wavelength). For example, tosubstantially match the dispersion of the fiber optic, the materialrefractive index preferably lies within about 0.5% of the effective moderefractive index; more preferably within about 0.2%, and mostpreferably, within about 0.15%. In addition, for dispersion matching, aslope which is substantially the same as that of the fiber optic is onehaving a value that is preferably within about 25%, for example, of thefiber optic slope.

Material dispersion of polymer composition 60, as well as the value ofthe material refractive index, are controlled by altering the amount ofthe infrared absorbing dye present in the polymer composition. Thus, thematerial dispersion across the wavelength band can be controlled tosubstantially match or mismatch the effective mode dispersion of theoptical fiber. Also, addition of the dye raises the value of thematerial refractive index (relative to the base refractive index), andit can be controlled to lie within the aforementioned preferablepercentage, if desired. Thus, the amount of dye present in thecomposition (as well as the composition of the polyolefin) controls thematerial refractive index.

In addition, the spectral response of optical device 100 across thewavelength band can be controlled by controlling the material dispersionrelative to the effective mode dispersion. When the material dispersionsubstantially matches the effective mode dispersion, the spectralresponse of the device is substantially uniform. In the case of avariable optical attenuator, for example, a substantially uniformspectral response would mean that the attenuation level remains constantto within about 0.5 dB over the wavelength band of interest

The method may also include the step of varying the material refractiveindex of polymer composition 60 to a desirable refractive index withoutaltering the dispersion of the polymer composition 60. For example, thematerial refractive index may be controllably varied by controllablychanging the temperature of the composition, i.e. an increase intemperature will decrease the material refractive index, and a decreasein temperature will cause an increase. Because the temperature of thepolymer composition affects its material refractive index withoutaltering the material dispersion, the amount of light propagating fromside-polished fiber optic 30 to polymer composition 60, for example, canbe controllably varied while maintaining uniform device performance.This is important in a variable optical attenuator where maximum opticalenergy can be extracted from the fiber when the material refractiveindex of the polymer composition is substantially the same as thefiber's effective mode refractive index. In FIG. 5a, a controllableheating element 80 is included with optical divide 100 for providing achangeable temperature stimulus to material 60 in accordance with acontrol stimulus 105.

Side-polished optical fiber 30 of FIGS. 5a-b may be fabricated byconventional lapping and polishing techniques. Using this technique, thefiber is typically embedded in a fused silica substrate block 20containing a controlled radius groove. Material is carefully removedfrom a portion of fiber cladding 50 until core 40 is approached. At thispoint, the evanescent field of the optical energy propagating throughthe optical fiber can be accessed through surface 65 and propagatethrough polymer composition 60. The device interaction length can becontrolled by the remaining cladding thickness and the groove's radiusof curvature.

Alternatively, side-polished optical fiber 30 of may be fabricatedwithout the incorporation of substrate block 20 by the techniquedisclosed in the aforementioned commonly assigned U.S. patentapplications entitled “Blockless Fiber Optic Attenuators and AttenuationSystems Employing Dispersion Controlled Polymers” and “BlocklessTechniques for Simultaneous Polishing of Multiple Fiber Optics”, both ofwhich are being filed concurrently herewith.

While the invention has been particularly shown and described withreference to preferred embodiment(s) thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

We claim:
 1. A method for controlling material dispersion in a polymercomposition across a wavelength band, said method comprising the stepsof: (a) providing a portion of an optical fiber through which opticalenergy can propagate, wherein said portion of said optical fiber has asurface through which at least some of said optical energy can beextracted, and wherein said portion of said optical fiber has aneffective mode refractive index at each wavelength of said wavelengthband and an effective mode dispersion across said wavelength band; (b)forming said polymer composition over said surface of said portion ofsaid optical fiber, wherein said polymer composition comprises: (1) fromabout 0.2 to about 4% by weight of an infrared absorbing dye having anabsorption maximum from about 900 to about 1200 nm; and (2) from about96 to about 99.8% by weight of a polar olefin copolymer comprisingmonomeric units derived from two or more polar olefins having an ester,benzene or halogen substituent attached thereto; and wherein saidpolymer composition has a material refractive index at each wavelengthof said wavelength band and a material dispersion across said wavelengthband; and (c) controlling said material dispersion across saidwavelength band by altering the amount of said infrared absorbing dyepresent in said polymer composition, whereby said material refractiveindex at each wavelength is also controlled.
 2. The method of claim 1,wherein said polymer composition is formed by the steps of: (i)polymerizing said two or more polar olefins having an ester, benzene, orhalogen substituent attached thereto to form said polar olefincopolymer; and (ii) adding to said polar olefin polymer of step (i) fromabout 0.2 to about 4% by weight of said infrared absorbing dye having anabsorption maximum from about 900 to about 1200 nm, wherein said polarolefin copolymer is present in said polymer composition in an amountthat is from about 96.0 to about 99.8% by weight; wherein said materialdispersion and said material refractive index are controlled by alteringthe amount of said infrared absorbing dye added in step (ii).
 3. Themethod of claim 1, wherein said material dispersion in said polymercomposition substantially matches said effective mode dispersion in saidoptical fiber, wherein said material refractive index is substantiallythe same as said effective mode refractive index, and wherein the changein said material refractive index across said wavelength band issubstantially the same as the change in said effective mode refractiveindex across said wavelength band.
 4. The method of claim 3, whereinsaid material refractive index is controlled to lie within about 0.5% ofsaid effective mode refractive index and said change in said materialrefractive index across said wavelength band is within about 25% of saidchange in said effective mode refractive index across said wavelengthband.
 5. The method of claim 4, wherein said material refractive indexis within about 0.2% of said effective mode refractive index.
 6. Themethod of claim 1, wherein said wavelength band is from about 1500 nm toabout 1600 nm.
 7. The method of claim 1, further comprising the step ofaltering said material refractive index to a desirable refractive indexwithout changing said material dispersion.
 8. The method of claim 7,wherein said material dispersion in said polymer compositionsubstantially matches said effective mode dispersion in said opticalfiber and said desirable refractive index is substantially the same assaid effective mode refractive index.
 9. The method of claim 7, whereinsaid desirable refractive index is obtained by controllably changing thetemperature of said polymer composition formed on said optical fiber.10. The method of claim 1, wherein said infrared absorbing dye isselected from the group consisting of(8-((3-((6,7-dihydro-2,4-diphenyl-5H-1-benzopyran-8-yl)methylene)-2-phenyl-1-cyclohexen-1-yl)methylene)-5,6,7,8-tetrahydro-2,4-diphenyl-1-benzopyryliumtetrafluoroborate;bis[1,2-(4-dibutylaminophenyl)-1,2-ethylenedithiolate]nickel;bis[1,2-[4-(ethyl heptyl amino)phenyl]-1,2-ethylenedithiolate]nickel;bis[1,2-(4-dibutylaminophenyl)-1,2-ethylenedithiolate]platinum; andbis[1,2-[4-(ethyl heptyl amino)phenyl]-1,2-ethylenedithiolate]platinum,and wherein said two or more polar olefins are selected from the groupconsisting of tetrafluoropropyl acrylate, tetrafluoropropylmethacrylate,butyl acrylate, hexyl acrylate, trifluoroethyl methacrylate, laurylacrylate, pentafluorostyrene, pentafluorophenyl acrylate, methylacrylate, N,N-dimethylacrylamide, pentafluorophenyl methacrylate, methylmethacrylate, and vinylidene chloride.